Reflectors and the like of automobiles are produced by preparing corresponding moldings using various plastics, such as polypropylene and polycarbonates, and causing a metal, such as aluminum, to be vacuum-evaporated on the surface thereof. In such a case, however, if aluminum or the like metal is directly evaporated on the moldings made of plastics, the brightness of the metal is lost and those optical characteristics which are required of reflectors cannot be developed. Therefore, prior to metal evaporation, an under coating is applied in advance to the plastic surface and then cured to improve the optical characteristics. As the under coating to be used for such purposes, various ones are known, for example acrylic resin lacquers and nitrocellulose resin lacquers, urethane resin coatings and ultraviolet-curable coatings.
However, in applying these under coatings to plastic substrates, it is necessary to prepare different under coatings according to different plastics species. In other words, while these under coatings can suitably be applied to moldings made of plastics other than polypropylene, these under coatings, when applied to moldings made of polypropylene, can hardly develop a good adhesion between the substrates and under coatings and, therefore, another under coating for the exclusive application to moldings made of polypropylene must be prepared separately from these coatings. When such under coating for exclusive use is applied to moldings made of another plastic, for example a polycarbonate, the heat resistance decreases and the moldings cannot be used suitably as automotive reflectors and the like.
Meanwhile, an ultraviolet-curable liquid under coating composition for metal evaporation on FRPs which comprises a polyfunctional acrylate of dipentaerythritol and an isocyanurate form polyisocyanate is described in Japanese Kokai Publication Hei-07-26167, and an ultraviolet-curable liquid under coating composition for metal evaporation on FRPs, which comprises a compound having at least two (meth)acryloyl groups within the molecule, an oil-modified alkyd resin and a photopolymerization initiator is described in WO 95/32250. By applying these liquid compositions, as under coatings, to the surface of FRP (fiber-reinforced composite material) materials, it is intended to improve the adhesion to FRP materials, the heat resistance and the water resistance.
However, it is unknown whether these liquid compositions are adequately applicable to various plastics such as polypropylene, polycarbonates, polyethylene terephthalate, polybutylene terephthalate and acrylonitrile-butadiene-styrene copolymers. Therefore, the advent of a curable under coating for metal evaporation which is appropriately applicable to moldings made of various plastics and is excellent in adhesion to substrates and can give product moldings excellent in heat resistance, and a method of coating a plastic molding using that coating, for example a coating method suited for use in producing automotive reflectors or the like made of various plastic substrates, has been demanded.